Commonly used living body authentication apparatuses using fingerprints, which are a kind of living body feature, to authenticate individuals employ a method using a critical angle of total reflection by a triangular (optical) prism (for example, see Patent literature 1). The method involves reading bumpiness (ridges and furrows) of a skin surface, which enables a fingerprint image to be easily obtained with high contrast. The method has thus highly compatible with “fingerprinting” wherein fingerprints are collected by impressing an inked fingertip against paper, and the method has been used in judicial and police purposes.
On the other hand, there are recently increasing criminal acts, including use of a fake finger fabricated from resin such as silicone, and “identity theft” by attaching a semitransparent bumpy film imitating fingerprints to a real fingertip to pretend to be someone else. Detection of such an act may involve acquiring a high-contrast image having high contrast for matching fingerprints or the like, and in addition, a natural image of fingers that is similar to visual observation for detecting a counterfeit, and visually verifying these images.
Accordingly, there has been proposed an authentication apparatus using a contactless method in which fingers do not touch a prism, and acquiring a fingerprint image similar to natural visualization by naked eyes to achieve authentication (for example, see Patent literature 2).